Such an auxiliary steering is known as steering rack auxiliary power steering from EP-B1-01 92 641. To prevent leakage losses at the inlet-seat valves, their closing springs are made comparatively strong. Different activation forces result for the purpose of opening the inlet-seat valves, on the one hand, and the outlet-seat valves, on the other hand. A relatively high activation moment is required on the manual steering wheel upon initiating the steering movement so as to build up pressure; that is because the force of the closing spring must also overcome the force of the centering spring. On the other hand, only the force of the centering spring is important when it comes to reducing the pressure in the servomotor. That makes steady adjustment of the pressure difficult because the activation force constantly fluctuates back and forth between turn-on and turn-off force and the driver gets the feeling that the steering sticks.
The steering valve is known from a steering rack auxiliary power steering. Such a steering valve can be used with the same effect in other auxiliary power steering apparatus, for example, in a ball-nut auxiliary power steering apparatus.